Not sure if it is a recent fad but my ukes that have X-bracing sound great. I do think it's the builder that is key here. I think any bracing would sound good but really depends on the builder's design. The moon birds/koa birds have x-bracing and they sound fabulous, in resonance, tone, and volume. My cedar bird is a canon and has tone as smooth as butter. Again, the bird series is based on a custom builders design in Japan by the name of Mitsuta Morihiko. I think the Anuenue X-bracing sounds better than the fan bracing (which also sounds very very good) of their anuenue series (AMM, AKK, PAS, Dream). But there is a significant price difference.
Also, pono has a new lattice bracing with their master series that sounds fantastic. I think they should use this bracing on all their pono ukes...
Builder over bracing is important.